This invention relates generally to cranes; more specifically relates to cranes which rotate around a central axis, such as jib cranes; and still more specifically relates to cranes having a rotatable vertical mast.
The cranes having a rotatable mast such as the jib cranes described in our said prior application comprises a base assembly, an upright column or mast which may have a wide flange or "I" beam structural shape rotatably mounted to the base assembly, and a horizontally extending boom or load beam rigidly secured to the upper end of the mast. A trolley including a hoist is movably mounted on the load beam. The trolley and hoist may be operated by electric or hand power. The bottom part of the mast is positioned inside a hollow structural member such as a pipe and spaced from the inside surface thereof, and rotatably associated therein. Force transfer means, such as roller means, were rigidly secured to the mast. The rollers frictionally contacted the pipe and revolved around the circumference of the pipe as the mast and load beam rotated around the central axis of the pipe.
In order to properly position the roller means, a section was cut out from the mast column and the holder or cage containing the roller means was welded or otherwise rigidly attached to the mast. Prior to making such attachment, the roller means were positioned to provide the proper contact with the pipe and also the proper plumbness of the mast. Alternatively, two rollers housed in separate cages could be used and secured to the column without requiring a section to be cut from the column.
The subject invention still further simplifies the force transfer means by providing a bearing boot to replace the roller means, and the bearing is rigidly secured to the column structure of the mast and frictionally contacts the inside surface of the pipe, as the mast rotates. The bearing boot revolves in a sliding manner on the pipe surface. The boot appreciably reduces the labor required for constructing and assembling the crane, as compared with the crane system having the roller means.
In the prior jib crane systems, the rotating of the load beam, from time to time, generated excessive lateral forces causing instability and "kick up" of the mast. In the present invention, a guard or baffle is mounted to the mast at a position substantially opposed to the force transfer means (roller means or bearing boot), to provide stability and prevent "kick up" of the mast.